With a storage device mounted on a portable apparatus, restrictions on power consumption are severe due to being driven by a battery. Especially, a lower power consumption when no access is being made to a storage, that is, during standby, is highly preferred. In a state during the standby in a low power consumption mode, there are several stages according to easiness of recovery upon a subsequent occasion when an access becomes necessary. Among such, in a low power consumption mode with the least power consumption aside from power being off, power of almost all components, such as a communication link, as well as a volatile main storage, a processor, an oscillation circuit and the like on a storage device side, is turned off. Due to this, management information that is necessary for the recovery when a host restarted accessing is saved from a volatile main storage to a non-volatile auxiliary storage device before transitioning to the low power consumption mode.
Although transition and recovery to and from the low power consumption mode need to be performed promptly, the management information that should be saved is quite large. Due to this, a flash memory, such as of a NAND type, that is cheap and has relatively fast read performance is suitable as the auxiliary storage device. However, a flash memory is a memory device with a limited number of rewrites, and damages such as a write failure and a data read error occur when a large number of rewrite operations has been performed.
Due to this, in a case where a transition order to the low power consumption mode is frequently given from a host side, an amount of the power consumption increases to the contrary due to repeated transitions and recoveries to and from the low power consumption mode. Further, the flash memory is worn out by the frequent occurrences of rewrites in the flash memory.